The inhibiting action of intrinsic impurities in natural calcium carbonate minerals to their dissolution kinetics in aqueous H2O–CO2 solutions

We have measured the surface controlled dissolution rates of natural calcium carbonate minerals (limestone and marble) in H₂O–CO₂ solutions by using free drift batch experiments under closed system conditions with respect to CO₂, at 10°C with an initial partial pressure of carbon dioxide of 5 · 10⁻² atm. All experiments revealed reaction rates F, which can be described by the empirical relation: F_n1 = k_n1 · (1 − c/c_eq)^n₁ for c < c_s, which switches to a higher order n₂ for calcium concentrations c ≥ c_s described by F_n2 = k_n2 · (1 − c/c_eq)^n₂. k_n1 and k_n2 are rate constants in mmole/(cm² · s), c_eq is the equilibrium concentration with respect to calcite. The values of the constants n₁, n₂, k_n1, k_n2 and c_s depend on the V/A ratio employed, where V is the volume of the solution and A is the surface area of the reacting mineral. Different calcium carbonate minerals exhibit different values of the kinetic constants. But generally with increasing V/A, there is a steep variation in the values of all kinetic constants, such that the rates are reduced with increasing V/A ratio. Finally with sufficiently large V/A these values become constant. These results are explained by assuming intrinsic inhibitors in the bulk of the mineral. During dissolution these are released from the calcite matrix and are adsorbed irreversibly at the reacting surface, where they act as inhibitors. The thickness d of the mineral layer removed by dissolution is proportional to the V/A ratio. The amount of inhibitors released per surface area is given by d · c_int, where c_int is their concentration in the bulk of the mineral. At low thicknesses up to ≈3 · 10⁻⁴ cm in the investigated materials, the surface concentration of inhibitors increases until saturation is attained for thicknesses above this value.To analyze the surface concentration and the type of the inhibitors we have used Auger spectroscopy, which revealed the presence of aluminosilicate complexes at the surface of limestone, when a thickness of d ≈ 10⁻³ cm had been removed by dissolution. In unreacted samples similar signals, weaker by one order of magnitude, were observed. Depth profiles of the reacted sample obtained by Ar-ion sputtering showed the concentration of these complexes to decrease to the concentration observed in the unreacted sample within a depth of about 10 nm. No change of the concentration with depth was observed in unreacted samples. These data suggest that complexes of aluminosilicates act as inhibitors, although other impurities cannot be excluded.     

Experimental identification of CO2–oil–brine–rock interactions: Implications for CO2 sequestration after termination of a CO2-EOR project

Carbon dioxide enhanced oil recovery (CO₂-EOR) has been widely applied to the process of carbon capture, utilization, and storage (CCUS). Here, we investigate CO₂–oil–water–rock interactions under reservoir conditions (100 °C and 24 MPa) in order to understand the fluid–rock interactions following termination of a CO₂-EOR project. Our experimental results show that CO₂-rich fluid remained the active fluid controlling the dissolution–precipitation processes in an oil-undersaturated sandstone reservoir; e.g., the dissolution of feldspar and calcite, and the precipitation of kaolinite as well as solid phases comprising O, Si, Al, Na, C, and Ti. Mineral dissolution rates were reduced in the case that mineral surfaces were coated by oil. Mineral wettability and composition, and oil saturation were the main controls on the exposed surface area of grains, and mineral wettability in particular led to selective dissolution. In addition, the permeability of the reservoir decreased substantially due to the precipitation of kaolinite and solid-phase particles, and due to the clogging of less soluble mineral particles released by the dissolution of K-feldspar and carbonate cement, whereas porosity increased. The results provide insight into potential formation damage resulting from CO₂-EOR projects.     

Modelling the Mont Terri HE-D experiment for the Thermal–Hydraulic–Mechanical response of a bedded argillaceous formation to heating

Coupled thermal–hydrological–mechanical (THM) processes in the near field of deep geological repositories can influence several safety features of the engineered and geological barriers. Among those features are: the possibility of damage in the host rock, the time for re-saturation of the bentonite, and the perturbations in the hydraulic regime in both the rock and engineered seals. Within the international cooperative code-validation project DECOVALEX-2015, eight research teams developed models to simulate an in situ heater experiment, called HE-D, in Opalinus Clay at the Mont Terri Underground Research Laboratory in Switzerland. The models were developed from the theory of poroelasticity in order to simulate the coupled THM processes that prevailed during the experiment and thereby to characterize the in situ THM properties of Opalinus Clay. The modelling results for the evolution of temperature, pore water pressure, and deformation at different points are consistent among the research teams and compare favourably with the experimental data in terms of trends and absolute values. The models were able to reproduce the main physical processes of the experiment. In particular, most teams simulated temperature and thermally induced pore water pressure well, including spatial variations caused by inherent anisotropy due to bedding.     

Hydrological situation of a typical watershed in the Loess Tableland Area of China over the past 30 years

Due to deficient water resources in the Loess Plateau, watershed management plays a very important role, not only for ecological and environmental protection but also for the social development of the region. To better understand the hydrological and water resource variations in the typical watershed of the Loess Plateau and the Qinghe River Basin, the influences of land cover and climate change were analysed, and a SWAT model was built to simulate the response of the hydrological situation to land cover changes that have occurred over the past 30 years. The results demonstrated that the main land cover change occurring in the Qinghe River Basin was the conversion of land cover from grassland to woodland and farmland from the late 1980s to 2010. Woodland and farmland took 87.36 and 10.55%, respectively, from the overall area transferred over 20 years and more than 18% of the total watershed area. Hydrological simulation results indicated that land cover played a predominant role in the hydrological variation of the Qinghe River Basin, although the effects of climate change should not be discounted. The significant changes in land cover could be superimposed by policy orientation and economic requirements. Although it is hard to evaluate the land cover changes and the corresponding hydrological responses in a simple language, related analyses have demonstrated an increasing trend of runoff in the dry season, while there is a somewhat decreasing trend during the flood season in the river basin. There results could be significant and provide a positive influence on both future flood control and the conservation of water and soil.     

Hornblende–garnet–plagioclase thermobarometry: a natural assemblage calibration of the thermodynamics of hornblende

Calibrations are presented for an independent set of four equilibria between end-members of garnet, hornblende, plagioclase and quartz. Thermodynamic data from a large internally-consistent thermodynamic dataset are used to determine the ΔG° of the equilibria. Then, with the known mixing properties of garnet and plagioclase, the non-ideal mixing in amphibole is derived from a set of 74 natural garnet–amphibole–plagioclase–quartz assemblages crystallised in the range 4–13 kbar and 500–800 °C. The advantage of using known thermodynamic data to calculate ΔG° is that correlated variations of composition with temperature and pressure are not manifested in fictive derived entropies and volumes, but are accounted for with non-ideal mixing terms. The amphibole is modelled using a set of ten independent end-members whose mixing parameters are in good agreement with the small amount of data available in the literature. The equilibria used to calibrate the amphibole non-ideal mixing reproduce pressures and temperatures with average absolute deviations of 1.1 kbar and 35 °C using an average pressure–temperature approach, and 0.8 kbar with an average pressure approach. The mixing data provide not only a basis for thermobarometry involving additional phases, but also for calculation of phase diagrams in complex amphibole-bearing systems. Received: 8 November 1999 / Accepted: 7 July 2000     

Seismic triggering of atmospheric variables prior to the major earthquakes in the Middle East within a 12-year time-period of 2002–2013

Several studies have reported the increased values of surface-latent heat flux (SLHF) and rainfall events prior to the earthquakes as the seismic precursors. In order to investigate the variation of two mentioned atmospheric variables, we analyzed 39 major earthquakes in the Middle East based on the time series of NASA remote sensing data. On this basis, we observed that accumulated rainfall and SLHF of about 29 earthquakes were higher than 10 mm and 50 W/m², respectively (~75 %), over 3–23 days prior to the main shock of major earthquakes. We believed that the records of atmospheric variables are the consequence of a seismic-triggered chain including of air ionization, surface-latent heat exhalation, water vapor condensation and subordinate rainfall as the atmospheric responses to lithospheric motions. This seismic triggering in the Middle East has averagely caused to accumulated rainfall of ~35 mm and maximum SLHF of ~115 W/m² over the 3–23 days prior to 39 major earthquakes. To investigate of spatial correlation between earthquakes and atmospheric variations, we clustered 39 major earthquakes in eight seismological regions. Then, we estimated the moderate and strong correlation (R ²) between preceding times of earthquakes with magnitude of major earthquakes and their hypocenter depth equal to 0.48 and 0.68, respectively.     

Identifying urban–rural differences in social vulnerability to natural hazards: a case study of China

Identifying and analyzing the urban–rural differences of social vulnerability to natural hazards is imperative to ensure that urbanization develops in a way that lessens the impacts of disasters and generate building resilient livelihoods in China. Using data from the 2000 and 2010 population censuses, this study conducted an assessment of the social vulnerability index (SVI) by applying the projection pursuit cluster model. The temporal and spatial changes of social vulnerability in urban and rural areas were then examined during China’s rapid urbanization period. An index of urban–rural differences in social vulnerability (SVI_D) was derived, and the global and local Moran’s I of the SVI_D were calculated to assess the spatial variation and association between the urban and rural SVI. In order to fully determine the impacts of urbanization in relation to social vulnerability, a spatial autoregressive model and Bivariate Moran’s I between urbanization and SVI were both calculated. The urban and rural SVI both displayed a steadily decreasing trend from 2000 to 2010, although the urban SVI was always larger than the rural SVI in the same year. In 17.5% of the prefectures, the rural SVI was larger than the urban SVI in 2000, but was smaller than the urban SVI in 2010. About 12.6% of the urban areas in the prefectures became less vulnerable than rural areas over the study period, while in more than 51.73% of the prefectures the urban–rural SVI gap decreased over the same period. The SVI_D values in all prefectures had a significantly positive spatial autocorrelation and spatial clusters were apparent. Over time, social vulnerability to natural hazards at the prefecture-level displayed a gathering–scattering pattern across China. Though a regional variation of social vulnerability developed during China’s rapid urbanization, the overall trend was for a steady reduction in social vulnerability in both urban and rural areas.

     

Temporal–spatial variability of atmospheric and hydrological natural disasters during recent 500 years in Inner Mongolia,China

Natural Hazards - Inner Mongolia, located in the northern China, is a natural disaster-prone region. This study is dedicated to making a comprehensive and quantitative analysis of the...     

The response of the Gulf of Mexico to wind and heat flux forcing: What has been learned in recent years?

The Loop Current and its shed eddies dominate the circulation and dynamics of the Gulf of Mexico (GoM) basin. Those eddies are strongly energetic and are the cause of intense currents that may penetrate several hundred meters deep. However, there are regions in the GoM and periods of time in which the local atmospheric forcing plays an important role in its dynamics and thermodynamics. The circulation on the shelves, and particularly on the inner shelf, is mainly wind-driven with seasonality, changing direction during the year with periods of favorable upwelling/downwelling conditions. The wind-driven circulation is associated with the transport of waters with different temperature and salinity characteristics from one region to another. The interannual variability of the circulation on the shelves is linked to the atmospheric variability. Intraseasonal variability of the wind patterns considerably affects the likelihood and magnitude of upwelling and downwelling. The geometry of the GoM is such that large-scale winds may drive opposing upcoast/downcoast currents along different parts of the curving coast, resulting in convergence or divergence zones. The width of the shelves in the GoM is variable;while the West Florida Shelf, the Texas-Louisiana shelf and the Campeche Bank are more than 200 km wide, they are narrower near Veracruz and Tabasco. Another consequence of the GoM physiography and the wind forcing is the development of cross-shelf transports in the southern Bay of Campeche, the southern Texas shelf and southeast of the Mississippi river, which in turn vary during the year. During autumn-winter (from September to April), the GoM is affected by cold fronts coming from the northwest United States, which are associated with strong, dry, and cold winds that mix its waters and generate large sensible and latent heat fluxes from the ocean to the atmosphere. These frontal passages also cool the GoM surface waters due to mixing with lower temperature subsurface waters. During summer, tropical cyclones crossing the GoM can dramatically affect circulation and coastal upwelling.     

Social perception and response to the drought process: a case study of the drought during 2009–2010 in the Qianxi’nan Prefecture of Guizhou Province

Studies carried out on the drought process, which can be classed as a gradual disaster, can help us to understand the disaster mechanism and offer strategies for disaster prevention. This paper uses the example of the drought in the Qianxi??nan Prefecture of Guizhou Province from July 2009 to May 2010. Data have been collected from government gazetteers, meteorological monitoring data, and field surveys to build up a sequence of meteorological drought indices. The categorization of the victims?? perception of drought impact, and the stages of drought responses of different subjects (government, social organizations, and the public), has also been examined by the same way. By contrasting the differences between the metrological drought indices, and victims?? perception of drought impact, researchers explored the drought cognition features of victims, social response features, and dynamic relationships between drought development and social responses. The results were as follows: The drought evolution process could be divided into 6 phases, and victims?? perception of drought impact could be divided into 7 phases. They were consistent in time period, and the victims?? perception of drought was subjective and based on their direct experiences. Their response has the characteristics of long term and concentration on a time. The responses of government and social organizations obviously fell behind those of victims, but they were effective and intensive in both timescale and effort. As the drought developed, responses shifted from individual to social responses and from practical to economic, political, and technological responses. On the basis of the results, the author has suggested methods of preparing stakeholders against possible drought risks.     

Geochemical modelling of CO2–water–rock interactions in a potential storage formation of the North German sedimentary basin

The lower Triassic/Bunter sandstone and lower Jurassic/Rhät formations of the Northern Germany sedimentary basin constitute feasible reservoirs for the storage of CO₂ from combustion of fossil fuels or industrial production processes. This study presents analyses of geochemical interactions between CO₂, formation fluid and rock of these potential reservoirs using geochemical modelling in order to assess the short and long term impact of CO₂ sequestration. Batch equilibrium modelling was performed first for assessing the consistency of fluid and mineralogy field data and for identifying potential secondary minerals under the influence of injected CO₂. Inclusion of reaction kinetics in the batch models allowed an observation of reaction paths and to estimate the time frame of geochemical reactions. Finally, one-dimensional equilibrium reactive transport modelling was used in order to investigate the direction of reactions under conditions of fluid flow and mass transport and to quantify feedbacks of reactions on transport processes.Results of the simulations performed show that dawsonite may act as the main CO₂ storage mineral in both formations, while the carbonates calcite and dolomite dissolve over time. Also, changes in porosity and permeability are significant in the equilibrium reactive transport simulations. The time scale of kinetically controlled reactions observed in the kinetic batch modeling, however, suggests that CO₂ mineral trapping in both formations requires very long time frames, and hence other mechanisms such as structural or solubility trapping seem to be more relevant within the injection or early post-injection phase for the studied formations.     

Dissolution kinetics of selected natural minerals relevant to potential CO2-injection sites – Part 2: Dissolution and alteration of carbonates and feldspars in CO2-bearing brines

Chemical interaction processes among injected CO₂, saline fluids and potential reservoir materials are experimentally simulated to derive dissolution rates of natural materials (minerals) that can be used as input parameters for modeling of CO₂ storage in deep saline formations and risk analyses. In order to study dissolution processes, mineral aliquots were exposed to CO₂-bearing brines at elevated temperature (60, 100, 150 °C) and pressure (85 bar) and at various run durations. Several potential reservoir rocks include carbonates as cement. Calcite and dolomite grains were therefore mainly used as solid starting material. Experiments with the two feldspar varieties alkali feldspar and almost pure anorthite were performed in addition. Grain sizes of the mineral starting materials varied between <63 μm and 500 μm with most experiments performed at grain size fractions of 160 – 250 μm and 250 – 500 μm. All experiments run with a complex synthetic brine (total dissolved solids: ∼156 g/l) according to a natural upper cretaceous formation water. Dry ice was used as CO₂-source. All experiments were done in closed batch reactors. These reactors allow mimicking reservoir conditions far from the injection site as well as reservoir conditions after finishing the CO₂ injection. The concentration changes during the experiment were monitored by ICP-OES measurements of the initial and the post-run fluids. Dissolution rates were derived based on the concentration changes of the brine.Most of the studied experimental variables and parameters (temperature, run duration, grain size, brine composition – expressed as pH-value and ionic strength) impact alteration of the reacting agents, i.e. they change the chemical composition of the brine, change the surfaces of the mineral aliquots exposed to the CO₂-bearing brine, and induce formation of secondary minerals. Hence, all influencing parameters on dissolution processes have to be considered and time-resolved changes of the dissolution behavior have to be implemented in numerical simulations of processes at CO₂ injection sites and CO₂ storage reservoirs.     

Dispersion modeling of volcanic ash clouds: North Pacific eruptions, the past 40?years: 1970–2010

Over the last 40 years, there have been numerous volcanic eruptions across the North Pacific (NOPAC) region that posed a potential threat to both local communities and transcontinental aircraft. The ability to detect these volcanic clouds using satellite remote sensing and predict their movement by dispersion modeling is a major component of hazard mitigation. The Puff volcanic ash transport and dispersion model, used by the Alaska Volcano Observatory, was used to illustrate the impact that these volcanic ash clouds have made across the NOPAC and entire Polar region over the past 40 years. Nearly, 400 separate ash clouds were analyzed that were either reported or detected to have reached above 6 km (20,000 ft) above sea level, an average of one ash cloud every 1.25 months. Particular events showed that ash clouds can be tracked from Alaska to Greenland (Crater Peak, Mount Spurr in 1992), from Kamchatka to Alaska (Kluvicheskoi Volcano in 1994), from Alaska to California (Mount Cleveland Volcano in 2001) and from multiple events within 1 day (Mount Augustine Volcano in 2006). This study showed the vast number of events that have impacted this Polar region and how tracking them is useful for hazard mitigation.     

Laboratory Investigations of the Hydro-Mechanical–Chemical Coupling Behaviour of Sandstone in CO2 Storage in Aquifers

This paper is devoted to experimental investigations of the hydro-mechanical–chemical coupling behaviour of sandstone in the context of CO₂ storage in aquifers. We focused on the evolution of creep strain, the transport properties and the elastic modulus of sandstone under the effect of CO₂–brine or CO₂ alone. A summary of previous laboratory results is first presented, including mechanical, poromechanical and hydro-mechanical–chemical coupling properties. Tests were then performed to investigate the evolution of the creep strain and permeability during the injection of CO₂–brine or CO₂ alone. After the injection of CO₂–brine or CO₂ alone, an instantaneous volumetric dilatancy was observed due to the decrease in the effective confining stress. However, CO₂ alone had a significant influence on the creep strain and permeability compared to the small influence of CO₂–brine. This phenomenon can be attributed to the acceleration of the CO₂–brine–rock reaction by the generation of carbonic acid induced by the dissolution of CO₂ into the brine. The original indentation tests on samples after the CO₂–brine–rock reaction were also performed and indicated that the elastic modulus decreased with an increasing reaction time. The present laboratory results can advance our knowledge of the hydro-mechanical–chemical coupling behaviour of sandstone in CO₂ storage in aquifers.